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Hello Everyone,
I've a CentOS 7.3 system running Intel Xeon Phi 3120A coprocessor with an Intel Pentium Gold G5400 processor. I'm using Intel Compiler - ICC to compile C code included with OpenMP for parallel programming. I tested a simple code that calculates the value of Pi on this system. But the Pentium processor with its maximum thread capacity, which is 4 seems to be way faster than the coprocessor with 228 threads at its full capacity. I know the Pentium cores are faster than Xeon Phi cores, but given the number of thread count the Xeon Phi can provide I still can't understand the reason for this difference.
The code I used is as follows,
#include <stdio.h> #include <stdlib.h> #include <omp.h> static long num_steps = 100000; double step; int NUM_THREADS=228; void main() { #pragma offload target (mic:0) { int i,nthreads; double pi,sum[NUM_THREADS],t1,t2,time = 0.0; step = 1.0/(double)num_steps; t1 = omp_get_wtime(); omp_set_num_threads(NUM_THREADS); #pragma omp parallel { double x; int i; int ID = omp_get_thread_num(); int nthrds = omp_get_num_threads(); if(ID==0) nthreads = nthrds; for(i=ID, sum[ID]=0.0; i<num_steps; i=i+nthrds) { x = (i+0.5)*step; sum[ID] += 4.0/(1.0+x*x); } } for(i=0,pi=0.0;i<nthreads;i++)pi += sum*step; t2 = omp_get_wtime(); time = t2 - t1; printf("pi value:(%f)\n",pi); printf("time spent:(%f)\n",time); } }
I ran the code on the Pentium Gold processor removing the offload command and got the following result.
[root@localhost codes]# icc -qopenmp para_pi_mic.c -o para_pi_mic [root@localhost codes]# ./para_pi_mic pi value:(3.141593) time spent:(0.001684)
Then on the coprocessor, I got the following result,
[root@localhost codes]# icc -qoffload -qopenmp para_pi_mic.c -o para_pi_mic [root@localhost codes]# ./para_pi_mic pi value:(3.141593) time spent:(0.263586)
Here the time denotes the execution time for the parallelized code region.
Could you explain what's happening here, please.
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